Positive displacement rotary pump



Noy. 28, 1950 A. c. DURDIN, III

' POSITIVE DISPLACEMENT ROTARY PUMP 2 Sheets-Sheet 1 Filed Jan. 26, 1946 FIG-5 FIG.6 @l'j FIGZ T B L Nov. 28, 1950 A. c. DURDIN, 111 2,531,726

POSITIVE DISPLACEMENT ROTARY PUMP Filed Jan. 26, 1946 2 Sheets-Sheet 2 Q I Q 2 V I 2 *sl i \j g.-- 4 w 5 1 gr E i! Q Wk EII [-5 \K 2 I i. y X

Patented Nov. 28, 1950 POSITIVE DISPLACEMENT ROTARY PUMP Augustus C. Durdin, III, Rockford, Ill., assignmto Geo. D. Roper Corporation, Rockford, Ill., a corporation of Illinois Application January 26, 1946, Serial No. 643,549

3 Claims.

. This invention relates to positive displacement rotary pumps.

The primary object oi my invention is (1) to improve the operating efllciency of pumps of this type, (2) to effect reduction in noise level, and (3) to enable the pumping elements to handle a wide range of viscous liquids without the attending consideration of changing speed and changing pump size to avoid cavitations, noises. and low operating efliciencies.

In furtherance of these objects my invention contemplates the provision of novel means to properly accelerate the inlet flow of liquid to the pumping elements, gears, vanes or lobes and to properly decelerate the flow of liquid discharged by the pumping elements. More par ticularly, my invention provides proportional means to keep the velocity of the liquid in step with the velocity of the pumping elements. In providing this condition I am enabled to cause the flow of liquid to pass through the pump with the minimum of energy loss due to turbulence, entrance loss, friction, and cavitation.

As applied to an external gear type rotary pump, another object of my invention is to provide improved means to accelerate liquid flow as it enters the pump to reach a velocity value equal to that of the gear rotation. whereby minimum energy is required to fill the gear cavities.

Another object is to provide uniform distribution of the liquid across the gear face or pumping element face, whereby to assure the minimum of recirculation of the liquid within the pumping cavity.

Another object is to provide an improved pumping action. in the case of gears, that is substantially quiet because of the absence of hydraulic shock and cavitation.

Still another object is to provide means for effecting acceleration and deceleration equal to the rotating speed of the gear or pumping element so that a wide range of viscous liquids can be pumped at the same rotating speed.

Other objects and attendant advantages will be appreciated by those skilled in this art as the invention becomes better understood by reference to the following description when considered in connection with the accompanying drawings, in which- Figure 1 is a vertical section through an external gear type rotating pump, on the centerline of the suction and discharge of the casing, embodying my invention;

Figure 2 is a horizontal sect on taken on the section line 2-2 of Figure 1 of the pump casing alone;

Figure 3 represents the shape and area. of the suction inlet opening A and the discharge outlet opening D, respectively, shown in Figure 2;

Figures 4 and 5 represent the shape and area of the suction inlet and suction outlet openings as at the section lines 44 and 5-5, respectively, of Figure 1;

Figure 6 represents the shape and area of the suction outlet opening B and the discharge inlet opening C, respectively, shown in Figures 1 and 2;

Figure '7 is a vertical section through the: pump substantially on the section line 1-1 of Figure 1; and

Figure 8 is a vertical section through the pump casing alone, substantially on the section line 1-1 of Figure 1.

The drawings show an illustrative embodiment.

of my inventionas applied to an external gear type pump. However, my invention in its broader aspect is applicable to all types of positive displacement rotary pumps.

In the embodiment shown the intermeshing pumping gears II and I2 are of the spiral type, although any posit ve displacement pumping gears may be-used, The gears have a running fit with reasonable clearance at the periphery in pump chambers l3 and I4. res ectively, in the pump casing which is designated generally by ii. In this case the pump chambers extend through from end to end of the casing, as shown in Figure 5. and the ends of the casing are finished flat and closed by a back plate l6 and a face plate l1. Locating pins l8 accurately position these lates on the pump'casing so as to properly align the pump bearings with the gear members. Suitable means, not shown, c amp the plates to the pump casing. In this instance the gear ii is fixed to drive shaft i9 and idler gear I2 rotates around idler shaft 2|. The drive shaft has suitable bearing support in the plates, and is provided with suitable packing means 22. The pump structure thus far described is conventional, and any suitable structure for a positive displacement rotary pump may be employed.

My invention provides a suction passage '23 and a discharge passage 24 for the pump, each having substantially the same shape characteristics except in reverse order, as shown in Figures 1 and 2. Each such passage is of Venturi shape along the vertical centerline as shown in Figure 1, that is, from the relatively large round inlet opening A to the relatively long, narrow outet opening B, and in reverse shape order at the discharge side as shown by the inlet discharge opening C gear or pumping cavities. such conditions of operation, the gear must be 3 and the outlet discharge opening D. As shown in the horizontal plane, Figure 2, the suction passage diverges from opening A to B and the discharge passage converges from opening C to D.

Also, in the preferred embodiment the narrow openings B and C merge into full length of the gears and gear chambers. Suction and discharge pipes 25 and 26, respectively, connect to the corresponding ends of the pump casing and have an internal cross-section similar to the openings A and D. I

In operating, the velocity of flow of the liquid at A is-equal-to that of the connected pipe line. In good practice, this does not exceed 6 feet per second for liquids having a maximum viscosity of 1,000 SSU. As the liquid enters the Venturi passage 23 the velocity flow is accelerated to a maximum value at B. This maximum value of velocity at B is equal to or slightly more than the peripheral velocity of the gear H. In actual practice in accordance with my invention, gear peripheral velocities in excess of 20 feet per secand have been used with complete success. To establish this velocity, requires a drop in head through the suction Venturi passage, at the inlet of the pump, of 5.5 inches mercury. The introduction of the accelerated liquid into the gear chambers at approximately the same speed as the gear peripheries results in-the minimum of hydraulic. shock and consequent minimum head loss to prime the gear cavities. It will be observed that the outlet B extends across the full width of the gears, the liquid being discharged through the opening B at the same velocity as the gear periphery, each cavity or pumping chamber of the gear is filled completely with the liquid. This action is a decided improvement over conventional design of inlet openings where, in most cases, care has been exercised to actually increase the area at the point of discharge to the gear from two to four times the initial area. This condition produces a serious degree of shock to accelerate the liquid at the gear from an abnormally low speed, say 1.5-2.0 feet per second to that of the periphery of the gear which may be 20 feet per second. This results in a substantial hydraulic loss, turbulence, and recirculation within the Furthermore, under slowed down considerably to permit practical operation of the pump when handling heavy viscous liquids. These objectionable conditions are overcome by my invention in which the Venturi suction passage of the character shown provides for orderly and predetermined acceleration of the liquid to a velocity equal to that of the gear. Similarly, at the discharge side, the discharging liquid is decelerated at a predetermined rate, with the same or similar advantages as described with reference to the suction side of the pump. The value of the Venturi passage at the discharge side of the gears is two fold, first, by gradually decelerating the liquid from the gear cavities a minimum loss in head is established, and secondly, a quieter liquid discharge is established due to the fact that a uniform gear face width pressure is present. This distinguishes from conventional discharge ports which are not free of turbulence, shock, and orderly deceleration, all of which contribute to noise, inefficiency, and limited operating speeds.

To handle heavy, viscous liquids with pumps according to my invention, it is only necessary that sufiicient absolute head is provided at the suction inlet to supply the necessary energy to accelerate the liquid to a velocity equal to that scribed above.

4 of the gear periphery. The absolute head required for this acceleration is a variable dependent on the viscosity of the liquid under flow. In

the case of oils in the range of 50,000 to 60,000

SSU, this head will exceed the available atmospheric pressure and, therefore, static positive heads will be required.

The principle of operation of my invention is exemplified by the following figures applying to the embodiment shown in the drawings: The inlet opening A and the discharge opening B each is .750 inch in diameter and has a cross section area of .4417 square inch. The Venturi section B and C at the suction and discharge, respectively, is 1.4375 inches long and .125 inch wide, a cross section area of .180 square inch. These area are shown in their proper proportions to produce the predetermined acceleration and deceleration de- Further applying the illustrative example, assume that the pump gears operate at 1750 R. P. M. With the outside diameter of the pump gears 1.125 inches, the speed of each gear at its periphery or outside diameter is 8.60 feet per second. The theoretical displacement of the gearsin this pump is equal to 5 gallons per minute at 1750 R. P. M. This figure is obtained by multiplying the number of teeth in each gear by the unit capacity of each tooth cavity and the revolutions per minute. At 5 gallons a minute of flow passing through inlet opening A the velocity of the liquid flow will equal 3.63 feet per second. The change in cross section area between A and B from .4417 square inch to .18 square inch in the suction passage shown produces an acceleration in velocity of flow of the liquid from 3.63 to 8.85 feet per second. Referring to the velocity of the gears at their periphery, 8.6 feet per second, it will be apparent that the liquid as it leaves the opening B and enters the gear chamber is traveling at a velocity approximately (in this instance slightly in excess) that of the periphery of the gears.

I claim:

1. A positive displacement rotary pump comprising a casing having a pump chamber, a rotary pumping element in said chamber rotating about an assumed horizontal axis at a preselected speed, and suction and discharge passages communicating with said chamber, the suction passage having a large inlet opening of predetermined cross section area with relation to the cross section area of its outlet opening, said passage converging and diverging in a vertical plane in Venturi shape and diverging in a horizontal plane and terminating in a narrow outlet opening in communication with the pump chamber and through which liquid enters the pump chamber, said vertical and horizontal planes being with respect to said horizontal axis, said outlet opening being elongated in a, horizontal plane, the discharge passage duplicating the shape of the suction passage including openings of the same dimensions as the openings in the suction passag but reversed so that the liquid is discharged from the pump chamber through the narrow opening and leaves the discharge passage through its large opening, said suction passage shaped to uniformly accelerate the flow of liquid to the pumping member by graduating the cross section area progressively from the inlet to the outlet of the passage so that the velocity of the liquid entering the pump chamber is substantially equal to the peripheral velocity of the pumping member, and the discharge passage shaped similarly to the suction passage but reversed to uniformly decelerate the flow from the pump chamber to its outlet opening so that the velocity of the liquid at the outlet opening of the discharge passage is the same as at the inlet opening of the suction passage.

2. A positive displacement rotary pump having a pumping member running in a pump chamber, a Venturi suction passage having a large opening for connection to a fluid supply and a narrow slit-like opening of preselected area in communication with the pump chamber extending substantially the full width of the pumping member, said passage shaped to uniformly accelerate the flow of liquid from the supply to the pumping member so that the velocity of the liquid entering the pump chamber is substantially equal to the peripheral velocity of the pumping member, and an inverse Venturi discharge passage from the pump chamber having a large opening of the same dimensions as the large opening in the suction passage for connection to a discharge line and a narrow slit-like opening of the same dimensions as the narrow slit-like opening in the suction passag in communication with the pump chamber, said discharge passage shaped to uniformly decelerate the flow of liquid discharged from the pump chamber to a preselected velocity less than the peripheral velocity of the pumping member.

3. A positive displacement rotary pump having a rotary gear type pumping member mounted for rotation in a pump chamber, a liquid supply pipe, a discharge pipe having the same size opening as the liquid supply pipe, a suction passage having an inlet opening conforming in cross section area with the delivery from said supply pipe and a narrow outlet opening elongated substantially the length or the gear member and discharging into said pumping chamber, said suction passage having a Venturi shape converging from said inlet opening to a minimum cross section area adjacent to the outlet opening and diverging in cross section area from said minimum area to said outlet opening to accelerate the liquid supply through said suction passage and deliver it to the pump chamber at avelocity substantially equal to the peripheral velocity of' the pumping member, and a discharge passage having an outlet opening conformingin cross sectional area with the discharge pipe and a narrow inlet opening elongated substantially the length of the gear member in communication with the pumping chamber, said discharge passage having a Venturi shape converging from said inlet opening to a minimum cross section area adjacent the inlet opening and diverging in cross section area from said minimum area to said outlet opening, said minimum cross section area in the discharge passage being of the same dimensions and shape as the minimum cross area in the suction tube and positioned the same distance from the inlet opening as the minimum area in the suction passage is spaced from the outlet opening from the pumping chamber whereby said discharg passage is shaped to decelerate the flow of liquid discharging from said pump chamber to said discharge pipe.

AUGUSTUS C. DURDIN, I11.

REFERENCES CITED The following references are of record in the file'ot this patent:

UNITED STATES PATENTS Number Name Date 621,280 Pitt Mar. 14, 1899 905,967 Wilkin Dec. 8, 1908 1,095,767 Adams May 5, 1914 1,407,496 Storey Feb. 21, 1922 FOREIGN PATENTS Number Country Date 2,686 Great Britain 1867 311,064 Italy Sept. 20, 1933 644,570 Germany Apr. 15, 1937 

